An old example of organic luminescence device is, e.g., one using luminescence of a vacuum-deposited anthracene film (Thin Solid Films, 94 (1982) 171). In recent years, however, in view of advantages, such as easiness of providing a large-area device compared with an inorganic luminescence device, and possibility of realizing desired luminescence colors by development of various new materials and drivability at low voltages, an extensive study thereon for device formation as a luminescence device of a high-speed responsiveness and a high efficiency, has been conducted.
As described in detail in, e.g., Macromol. Symp. 125, 1-48 (1997), an organic EL device generally has a structure comprising upper and lower two electrodes, and (a plurality of) organic compound layers including a luminescence layer between the electrodes formed on a transparent substrate.
For the luminescence layer, aluminum guinolynol complexes (a representative example thereof is Alq3 shown hereinafter), etc., having an electron-transporting characteristic and luminescence characteristic are used. For a hole-transporting layer, e.g., biphenyldiamine derivatives (a representative example thereof is α-NPD shown hereinafter), etc., having an electron-donative characteristic are used.
These devices have a rectifying characteristic, and when an electric field is applied between electrodes, electrons are injected from a cathode into the luminescence layer and holes are injected from an anode.
The injected holes and electrons are recombined within the luminescence layer to form excitons and cause luminescence when transferred to the ground state.
In this process, an excited state includes an excited singlet state and an excited triplet state, and the transition from the former state to the ground state is called “fluorescence” and the transition from the latter state to the ground state is called “phosphorescence”. And the substances in these excited states are called a singlet exciton and a triplet exciton, respectively.
In most of the organic luminescence devices studied heretofore, fluorescence caused by the transition from the excited singlet state to the ground state, has been utilized. On the other hand, in recent years, devices utilizing phosphorescence via triplet excitons have been studied.
Representative published literature may include:    Article 1: Improved energy transfer in electrophosphorescent device (D. F. O'Brien, et al., Applied Physics Letters, Vol. 74, No. 3, p. 422 (1999)); and    Article 2: Very high-efficiency green organic light-emitting devices based on electrophosphorescence (M. A. Baldo, et al., Applied Physics Letters, Vol. 75, No. 1, p. 4 (1999)).
In these articles, a structure including 4 lamination layers as organic layers sandwiched between electrodes has been principally used. Materials used therein include carrier-transporting materials and phosphorescent materials. Abbreviations for the respective materials are as follows.    Alq3: aluminum quinolinol complex    α-NPD: N4,N4′-di-naphthalene-1-yl-N4,N4′-diphenyl-biphenyl-4,4′-diamine    CBP: 4,4′-N,N′-dicarbazole-biphenyl    BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline    PtOEP: platinum-octaethylporphyrin complex    Ir(ppy)3: iridium-phenylpyrimidine complex

The above-mentioned Articles 1 and 2 both have reported devices exhibiting a high efficiency, including a hole-transporting layer comprising α-NPD, an electron-transporting layer comprising Alq3, an exciton diffusion-preventing layer comprising BCP, and a luminescence layer comprising CBP as a host material and ca. 6% of PtOEP or Ir(ppy)3 as a phosphorescent material dispersed in mixture therein.
Such a phosphorescent material is particularly noted at present because it is expected to provide a high luminescence efficiency in principle for the following reasons.
Excitons formed by carrier recombination comprise singlet excitons and triplet excitons in a probability ratio of 1:3. Conventional organic EL devices have utilized fluorescence of which the luminescence efficiency is limited to at most 25%, which has been an upper limit. However, if phosphorescence generated from triplet excitons is utilized, an efficiency of at least three times is expected in principle, and even an efficiency of 100%, i.e., four times, can be expected in principle, if a transition owing to intersystem crossing from a singlet state having a higher energy to a triplet state is taken into account.
Articles describing luminescence from the triplet state may include Japanese Laid-Open Patent Application (JP-A) 11-329739 (organic EL device and production process thereof), JP-A 11-256148 (luminescent material and organic EL device using the same), and JP-A 8-319482 (organic electroluminescent device).
However, like a fluorescent-type device, such an organic luminescence device utilizing above-mentioned phosphorescence is generally required to be further improved regarding the deterioration of luminescence efficiency and device stability.
The reason of the deterioration has not been fully clarified, but the present inventors consider deterioration occurs based on the mechanism of phosphorescence.
In the case where the organic luminescence layer comprises a host material having a carrier-transporting function and a phosphorescent guest material, a main process of phosphorescence via triplet excitons may include unit processes as follows:    1. transportation of electrons and holes within a luminescence layer,    2. formation of host excitons,    3. excitation energy transfer between host molecules,    4. excitation energy transfer from the host to the guest,    5. formation of guest triplet excitons, and            6. transition of the guest triplet excitons to the ground state and phosphorescence.        
Desirable energy transfer in each unit process and luminescence are caused in competition with various energy deactivation processes.
Needless to say, a luminescence efficiency of an organic luminescence device is increased by increasing the luminescence quantum yield of a luminescence center material, but it is also an important factor to increase its concentration. However, if the the concentration of luminescent excitons is too high, the luminescence intensity is rather lowered as also disclosed in JP-A 05-078655 or JP-A 05-320633. This phenomenon is known as concentration extinction or concentration deactivation. The reason for the phenomenon may be associated with radiationless transition with no luminescence due to progress of polymer formation reaction between luminescence center material molecules or those and their surrounding material molecules, as the above-mentioned competition reaction. Accordingly, it has been known that there is an appropriate concentration as a spatial density of luminescence excitons for improving a luminescence efficiency, irrespective of fluorescent material or phosphorescent material.
According to Article 3: Photophysics of metal-organic π-conjugated polymers, K. D. Ley et al., Coordination Chemistry Reviews 171 (1998), pp. 287-307, using a main chain-type polymeric compound comprising a metal complex segment, as a luminescent material, as a part of a main chain; photoluminescence is measured by using the following compound and application thereof to an organic luminescence device is also suggested.

However, according to experience of the present inventors, the above-mentioned main chain-type polymeric compound has an unstable C═O bond contained in Re complex, thus being considered to be lacking in stability as a compound. Further, the polymeric compound contains a polymer main chain including triple bond, thus also being considered to be lacking in photostability.
On the other hand, an embodiment using a side chain-type polymeric compound, represented by a formula shown below, having a metal complex segment in a polymer side chain as a phosphorescent material has been described in Article 4: Polymer electro-phosphorescent devices using a copolymer of Ir(ppy)2-bound 2-(4-Vinylphenyl)pyridine with N-vinylcarbazole, Change-Lyoul Lee et al., 3rd International Conference on Electroluminescence of Molecular materials and Related Phenomena, Program and Abstracts, 0-18, Sep., 5-8, 2001.

However, when a metal complex segment is introduced into a polymeric compound skeleton in the case where the metal complex segment has a conjugated structure, a conjugated (structure) proportion in the polymeric compound can readily be finally increased by constituting the polymer main chain skeleton with the conjugated structure rather than the case of having the metal complex segment in the side chain. By having a higher conjugated proportion in the polymeric compound, a higher electroconductivity is liable to be attained, thus allowing a preparation of a device possessing a high luminescence efficiency.